Many types of prosthetic devices have been developed over the years. In the early years, emphasis was placed on constructing an artificial limb which looked and moved much like a human limb. For example, many prosthetic devices were fabricated with a leg member and a foot member, with some form of pivoting member therebetween near the ankle region to allow the foot member to rotate about the ankle region. Elaborately constructed prosthetic devices were introduced, each attempting to simulate the natural movement of the human leg, ankle and foot. Though each of these attempts were intended to provide some level of normalcy to the artificial limb, they lacked the resilient energetic response needed for non-sedentary activities.
Various improvements have been made to prosthetic devices to enable the amputee to substantially increase his or her activity level. The advent of new materials, such as graphite composite materials, which are lightweight, strong, durable and relatively flexible, have been developed to further improve the performance of prosthetic devices. Also, contrary to earlier thinking, better compliance and energy response has been obtained by simplifying the structure of the prosthetic device rather than making it more complex. Prosthetic devices incorporating simple curved, flat, spring-like members have been developed which now enable amputees to participate in strenuous activities, such as tennis, basketball and jogging.
In particular, a prosthetic foot and leg device allowing a high degree of mobility on the part of an amputee was disclosed in applicant's U.S. Pat. No. 4,457,913 entitled "COMPOSITE PROSTHETIC FOOT AND LEG." That patent discloses a prosthetic foot and leg device utilizing a resin impregnated high-strength filament structure for the leg portion, foot portion and heel portion, with all three regions being provided with substantial elastic flexibility, of relatively low energy absorption characteristics, so as to give the wearer high mobility with a relatively natural feel. Contrary to earlier prosthetic devices which incorporated a rotatable or articulated ankle mechanism, this prosthetic device has no moving parts other than the inherent flexibility and energy response characteristics of the material itself.
That prosthetic device also has a substantially elastic leg portion, wherein the flexibility of the leg portion is in addition to the flexibility of the heel and foot portions. Though this flexibility provides additional energy storage and release, and gives the prosthesis increased resiliency and energy response, this additional flexibility in the leg makes the prosthesis somewhat springy, unlike the tibia and fibula of the human limb which are not flexible and elastic.
In U.S. Pat. No. 4,822,363, the applicant attempted to provide some rigidity to the shin portion so that the flexure would take place beneath the upper leg portion. However, as with the prosthetic device of the above-referenced patent, the flexibility and resiliency of the prosthetic device was built into the entire lower leg region, including the shin, foot, and heel portions, up to and including the bottom ten inches of the prosthetic device. It was thought that if the flexibility in the lower leg region was eliminated to any greater extent, the prosthesis would lose a valuable portion of its capacity to store and release energy. With at least ten inches of clearance between the lower extremity of the rigid shin portion and the ground, the curvature of the flexible shin and ankle regions was smooth and continuous, and the resiliency and energy response characteristics of this prior device was excellent, without stops or jolts during use. Furthermore, from a structural point of view, the smooth curvature of the shin and ankle regions could be adapted to have a substantial radius, thereby avoiding any stress concentrations in the prosthesis. Due to the gradual curve of a relatively large radius (in some cases the curve was complex and not a simple curve), the space beneath the curve member provided for a relatively long heel capable of demonstrating good resiliency and flexibility.
Nevertheless, the energy response of such previous devices was often too great for some patients, exceeding their particular needs. With certain geriatric or youth patients, the springiness of such prior devices was somewhat difficult to manipulate or control, reducing stability. Thus, there remains a need for a foot prosthesis which demonstrates good performance capabilities under a wide range of physical activities, but which at the same time provides enhanced safety, security, and control for the wearer.